This invention relates to an image transforming apparatus which changes an input image to form an output image, and more particularly to an image transforming apparatus wherein the output image is formed by mapping the input image onto a three-dimensional curved surface.
This type of a special effect device is known, for example, as disclosed in U.S. Pat. No. 4965844. In the special effect device a TV signal is converted into a digital signal, and an image appearing as if an input image is stuck to a three-dimensional surface (e.g., a cylindrical surface) is displayed on a display.
This type of image transforming method involves the steps of dividing the input image into blocks having predetermined sizes, sequentially storing image data of each block in a predetermined intra-memory address on the basis of a write address, executing a predetermined arithmetic operation with respect to the stored address of the input image data before being transformed on the basis of transform input data inputted by an operator through a separate input means, reading the block image data stored in the predetermined intra-memory address in accordance with a read address obtained as a result of the foregoing arithmetic operation when assembling the output image by a raster scan so that the output image appears as if the input image is stuck to a predetermined three-dimensional surface, and obtaining the output image consisting of such a two-dimensional plane that the input image is apparently transformed into a three-dimensional surface.
The read address value obtained as a result of the arithmetic operation is, because it directly represents the arithmetic result, not an address value predetermined in the memory but an address value having a fraction in some cases.
Hence, in this case, an interpolating means multiplies, respectively by predetermined coefficients, the image data of addresses in front of and in rear of the intra-memory address corresponding to the read address value having the fraction. Thereafter, those values are added to obtain the image data corresponding to the read address obtained as a consequence of the arithmetic operation.
However, for instance, an input image VDIN shown in FIG. 1A is wound on a cylindrical surface IM illustrated in FIG. 1B. In this case, folded segments TN of the input image VDIN are produced on the cylindrical surface IM. The image is folded back at the folded segments TN, resulting in such a state that the image on the display image is discontinuous. Therefore, in the folded segments TN, the addresses allocated to the respective blocks of the input image VDIN become discontinuous on an output image VDOUT1, with the result that the above-mentioned interpolation can not be done.
As a result of this, the fraction of the arithmetically obtained address value is omitted. The point at issue arise, wherein, as in the quality in FIG. 1B, the image for an output image does not assume a smooth line (or curve) at the folded segments TN; and instead, conspicuous stepped notches are formed therein, resulting in a deterioration of the output image.
Also, as the same reason, the point at issue arise, shown in FIG. 1C, stepped notches G1 are formed at the edge portion of cylindrical surface IM, resulting in a decline of the output image.